In recent years, in mobile communication systems such as mobile telephone devices, with diversity of service aspects, transmitting large volume data such as still images and moving images in addition to speech is demanded. Further, studies are underway on the MIMO communication system as a data transmission method of large volume data in the next-generation mobile communication system. The MIMO system provides a plurality of antennas on the transmitting side and the receiving side to transmit and receive a plurality of independent streams at the same time in the same band, so that it is possible to increase the throughput of the communication system without expanding the frequency band. In particular, with eigenmode transmission using array antennas, in the same frequency band, it is possible to transmit and receive independent signals formed with a plurality of eigenvectors at the same time.
Further, in the TDD (Time Division Duplex) system for cellular devices, adopting eigenmode transmission is studied (e.g., see Patent Document 1). FIG. 1 illustrates an image of communication using an eigenmode transmission scheme. Here, assume that radio transmitting apparatus 10 has M array antennas and radio receiving apparatus 20 has N array antennas (M and N are natural numbers equal to or greater than 2). Radio transmitting apparatus 10 forms eigenbeams B1 and B2 for transmission signals and performs transmission processing, and radio receiving apparatus 20 forms eigenbeams B3 and B4 for received signals and performs receiving processing.
In this case, response matrix A of the MIMO channel is expressed by following equations 1 to 5 using eigenvalue λi of eigenvector #i (i=1, 2, 3, . . . , M0).
                    [        1        ]                                                            A        =                                            E              r                        ⁢                          DE              t              H                                =                                    ∑                              i                =                1                                            M                0                                      ⁢                                                            λ                                i                            ⁢                              e                                  r                  ,                  i                                            ⁢                              e                                  t                  ,                  i                                H                                                                        (                  Equation          ⁢                                          ⁢          1                )                                          M          0                =                  min          ⁡                      (                          M              ,              N                        )                                              (                  Equation          ⁢                                          ⁢          2                )                                D        =                  diag          ⁡                      [                                                            λ                  1                                            ,                                                λ                  2                                            ,              …              ⁢                                                          ,                                                λ                                      M                    0                                                                        ]                                              (                  Equation          ⁢                                          ⁢          3                )                                          E          t                =                  [                                    e                              t                ,                1                                      ,                          e                              l                ,                2                                      ,            …            ⁢                                                  ,                          e                              t                ,                                  M                  0                                                              ]                                    (                  Equation          ⁢                                          ⁢          4                )                                          E          r                =                  [                                    e                              r                ,                1                                      ,                          e                              r                ,                2                                      ,            …            ⁢                                                  ,                          e                              r                ,                                  M                  0                                                              ]                                    (                  Equation          ⁢                                          ⁢          5                )            
Here, in equations 1 to 5, et,i is the eigenvector of radio transmitting apparatus 10 associated with eigenvalue λi of channel correlation matrix AHA, and er,i is the eigenvector of radio receiving apparatus 20 associated with eigenvalue λi of channel correlation matrix AAH.
By using this eigenmode transmission scheme, it is possible to increase the transmission capacity of the communication system without expanding the frequency band.    Non-Patent Document 1: “2.1. Uplink Sounding,” 3GPP TSG RAN WG1 #42, R1-051516, November 2005.